The present invention relates to a developing apparatus for use in a copying machine, a printer and so on.
In a conventional developing apparatus, developer is carried on a developing sleeve applied with a predetermined developing bias voltage and conveyed to a developing region, where the developer serves to develop an electrostatic latent image formed on an electrostatic latent image carrier. In order to triboelectrically charge the toner and to regulate a quantity of the toner, a developer regulating member is provided to come into contact with the developing sleeve.
In the case that non-magnetic toner is used as the developer, there has been a disadvantage that the toner is difficult to enter between the developing sleeve and the toner regulating member because of its poor fluidity, whereby a uniform toner layer can not be formed on the developing roller.
In order to eliminate the above disadvantage, Japanese patent publication 5-19145 proposes a developing apparatus in which an alternating voltage is applied to the developer regulating member to form an alternating electric field between the developing sleeve and the toner regulating member. In this developing apparatus, the alternating electric field causes micro-oscillation of the toner regulating member, allowing the non-magnetic toner of poor fluidity to smoothly enter between the developing sleeve and the toner regulating member, whereby a uniform toner layer can be formed on the developing roller.
Further, the conventional developing apparatus does not have sufficient compliance with a high density and high area-rate of image. Therefore, a toner consuming portion of an image print pattern is printed with a smaller quantity of toner than a toner non-consuming portion due to insufficient compliance when the toner consuming portion reaches a developing region, causing a ghost (negative-memory). If there is a solid image or the like before a half-tone image, the toner quantity is reduced, whereby dots can not be reproduced, resulting in an unclear image and bad tone reproduction.
To this end, in the conventional developing apparatus in which an alternating voltage is applied to the developer regulating member, it will be considered that not only the toner is sufficiently oscillated to be triboelectrically charged by enlarging the peak voltage of the alternating voltage or by making the frequency of the alternating voltage high, but also the toner is made movable to the developer carrying member by enlarging the potential difference between the direct current component of the developing bias applied to the developer carrying member and the direct current component of the blade bias applied to the toner regulating blade. However, both the developer carrying member and the developer regulating blade are made of conductive material and opposed to each other, which causes a leak at a potential difference of about 500V in accordance with the Pachen's law, resulting in image noise.
In order to reduce the maximum potential difference including the alternating component between the developing bias and the blade bias below 500v, the peak voltage difference is enlarged to activate the toner oscillation, the direct voltage difference would be made small. On the contrary, if movement of the toner to the developer carrying member is emphasized, the peak voltage difference would be made small. This means that the conventional developing apparatus is not enough to reduce the maximum potential difference between the developing bias and the blade bias below 500v. For example, even if the potential difference is reduced to 500V by using only a direct current component, the toner would not be oscillated and triboelectrically charged, resulting in no effect. Even if the potential difference of the direct component is reduced to 250V an alternating component having an amplitude of 500v is applied, enough effect would not be obtained.
In addition, a variation in toner fluidity due to deterioration of the toner caused by long-term printing or a variation in environment causes a variation in conveying quantity and charge property of the toner, which causes a problem that stability of tone reproduction could not be maintained until the end of apparatus life.